*Article* **Spatial Distribution, Contamination Levels, and Health Risk Assessment of Potentially Toxic Elements in Household Dust in Cairo City, Egypt**

**Ahmed Gad 1,\*, Ahmed Saleh 2,\*, Hassan I. Farhat <sup>3</sup> , Yehia H. Dawood <sup>1</sup> and Sahar M. Abd El Bakey <sup>4</sup>**


**Abstract:** Urban areas' pollution, which is owing to rapid urbanization and industrialization, is one of the most critical issues in densely populated cities such as Cairo. The concentrations and the spatial distribution of fourteen potentially toxic elements (PTEs) in household dust were investigated in Cairo City, Egypt. PTE exposure and human health risk were assessed using the USEPA's exposure model and guidelines. The levels of As, Cd, Cr, Cu, Hg, Mo, Ni, Pb, and Zn surpassed the background values. Contamination factor index revealed that contamination levels are in the sequence Cd > Hg > Zn > Pb > Cu > As > Mo > Ni > Cr > Co > V > Mn > Fe > Al. The degree of contamination ranges from considerably to very high pollution. Elevated PTE concentrations in Cairo's household dust may be due to heavy traffic emissions and industrial activities. The calculated noncarcinogenic risk for adults falls within the safe limit, while those for children exceed that limit in some sites. Cairo residents are at cancer risk owing to prolonged exposure to the indoor dust in their homes. A quick and targeted plan must be implemented to mitigate these risks.

**Keywords:** potentially toxic elements; indoor dust; pollution; exposure; risk assessment; urban; Cairo

### **1. Introduction**

Over the past few decades, a tremendous amount of hazardous waste materials has been released into various environmental media at increasing levels because of the rapid urbanization and globalization of economic and industrial activity [1–5]. Because the air in common is the primary carrier of fine particles, air pollution has produced a significant environmental impact (e.g., climate change and human health). The concentration of suspended particles in the air, which transports contaminants, especially potentially toxic elements (PTEs), has progressively increased, endangering humans. Because of their genotoxicity, carcinogenicity, chemical persistence, and non-degradability, PTEs attached to suspended particles would enrich in surface environments and have an acute or chronic impact on the health of vulnerable residents once they get into the human body [6–10]. PTEs can go through a human body via respiratory inhalation, ingestion of contaminated media, and dermal contact and accumulate over time [1,6,11,12].

Because indoor air can be significantly more polluted than outdoor air, it has captures remarkable attention from researchers. Imperfect air exchange and specific indoor emission sources combined with outdoor sources seems to be the leading causes of indoor air being a complex and contaminated environment [1,12]. People in megacities typically spend 80–90% of their own time indoors, in private homes, schools, and offices, potentially increasing their exposure to toxic substances being emitted from construction materials, household equipment, and electronic products, in conjunction with anthropogenic sources [13]. In

**Citation:** Gad, A.; Saleh, A.; Farhat, H.I.; Dawood, Y.H.; Abd El Bakey, S.M. Spatial Distribution, Contamination Levels, and Health Risk Assessment of Potentially Toxic Elements in Household Dust in Cairo City, Egypt. *Toxics* **2022**, *10*, 466. https://doi.org/10.3390/ toxics10080466

Academic Editor: Ilaria Guagliardi

Received: 26 July 2022 Accepted: 9 August 2022 Published: 11 August 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

this regard, the indoor ambiance and potential health risks inextricably associated with toxic substances' exposure in the indoor environment must be considered. Many scientific studies over the last decades have sufficiently demonstrated that prolonged exposure to contaminated indoor environments has undeniable fingerprints on serious health problems that result from direct and indirect exposure [6,7,12,13]. This direct impact on public health is extremely significant for children, who are more vulnerable to contaminant exposure due to increased hand-to-mouth interactions [1,4,14]. Furthermore, considerable advancements in analytical techniques used to investigate various biological samples will progressively improve exposure estimates for both healthy and at-risk populations [15,16].

There are numerous sources of indoor contaminants, the most significant of which is settled and suspended dust. Most of these hazardous and toxic pollutants are adsorbed to suspended particulates in indoor air and later deposited as house dust. Because of this process, the concentrations of contaminants in indoor dust are higher than their natural crustal concentrations [6,12]. Indoor dust is a motley mixture of inorganic and organic materials that can adsorb and concentrate PTEs [17,18]. This admixture would settle on the surfaces of residential objects (e.g., floors, carpets, furniture, and others) [19,20]. The main pathway for PTEs from outdoor sources into homes is the entry of contaminated suspended particles into outdoor air [20,21]. Many transporting methods bring street dust and soil materials indoors as a consequence of residents' activities (e.g., attached to shoes, clothes, bags, their pets, etc.) [7,12,22–24]. Moreover, considered external contaminated sources of indoor and household dust are suspended grains generated by industrial activities, road dust, traffic emissions, park soil, and other particles that are produced by outdoor activities [6,12]. Indoor dust PTE contamination has received a lot of attention owing to its significant effects on both residents' health and the environment [7,13,25]. One of the serious issues with indoor dust is that it is not exposed to the same processes that reduce its PTE concentrations as those that affect outdoor dust (e.g., diluting, leaching, or weathering). Consequently, indoor dust could be used as a long-term indicator of indoor environmental status [19].

Egypt has experienced severe soil, water, and air pollution in recent decades as deleterious consequences of rapid economic growth, urbanization, and increased energy demands [26–29]. Different studies were conducted to assess Egypt's air pollution. The vast majority of these studies have concentrated on the gaseous (CO, CO2, SO2, H<sup>2</sup> S, and NO2) and particulate matter [30–35]. Studies on indoor dust in Egypt have typically focused on major ions (SO4, NO3, Cl, NH4, Ca, Mg, Na, and K) [36], organic pollutants [37–40], and microorganisms [41–43]. There are limited studies on PTE contamination in indoor dust and their health risk assessments [23,24,44,45]. Moreover, no comprehensive geochemical study of Cairo City's indoor dust and the potential health risks for PTE exposure have been conducted. A notable lack of such necessary data might hinder the proper development of short and long-term policy initiatives towards reducing air pollution. More extensive research must be directed to thoroughly comprehend the detrimental health impacts of PTE air pollution. Findings and the conclusion of these surveys will be properly utilized to support the national policies and will contribute to the public health improvements. Therefore, the current study's specific objectives are to (1) detect the PTE levels in household dust and identify their spatial distribution in Cairo City; (2) assess the contamination levels using environmental indices; (3) identify the possible sources of PTEs in household dust using multivariate statistical analysis; and (4) assess the potential health risk for children and adults' exposure to PTEs.

#### **2. Materials and Methods**

#### *2.1. The Study Area*

Cairo (Al-Qhirah) is located in northern Egypt on the River Nile's right bank. It is Egypt's administrative center and the most sizable city in both Africa and the Middle East, and one of the world's most densely populated cities (9.9 million inhabitants). Many issues plague the city, including traffic congestion, air, soil, and water pollution, and ineffective

waste management [46]. Cairo is administratively divided into five chief regions (New Cairo, Eastern, Northern, Western, and Southern) (Figure 1; Table S1). fective waste management [46]. Cairo is administratively divided into five chief regions (New Cairo, Eastern, Northern, Western, and Southern) (Figure 1; Table S1).

Cairo (Al-Qhirah) is located in northern Egypt on the River Nile's right bank. It is Egypt's administrative center and the most sizable city in both Africa and the Middle East, and one of the world's most densely populated cities (9.9 million inhabitants). Many issues plague the city, including traffic congestion, air, soil, and water pollution, and inef-

*Toxics* **2022**, *10*, x FOR PEER REVIEW 3 of 23

**2. Materials and Methods** 

*2.1. The Study Area* 

**Figure 1.** Map displaying Cairo City and its administrative regions and sampling site's locations. **Figure 1.** Map displaying Cairo City and its administrative regions and sampling site's locations.

Cairo City has a typical Mediterranean climate, with different temperatures through seasons: winter 14 ◦C, spring 21 ◦C, summer 36 ◦C, and fall 23 ◦C. Most of the year, wind speeds range from 3 to 8 m/s. The north and northeast were dominant wind directions [47,48]. It is surrounded by agricultural and industrial activities. It contains the main industrial zones that exist in the Northern and Southern regions which host cement manufacturing plants, steel, oil and gas, quarrying, rubber, petrochemicals, metallurgical, textile, and plastic products [26,48].

#### *2.2. Sampling and Samples Preparation*

A total of 38 composite household settled dust samples were collected from different regions and districts in Cairo City in 2021 (Figure 1). The sample size was selected based on the major districts in Cairo City, in conjunction with budgetary constraints. To ensure a collection of representative samples at least 10 subsamples were collected from each main district representing a total of 473 private houses (1 sample per house) (Table S1 in Supplementary Materials). The undisturbed surfaces, such as cupboards, fans, bookshelves, and refrigerators, were slowly brushed using precleaned polyethylene brushes and plastic dustpans to collect dust samples, which were then carefully blended and placed into transparent, zip-locked, and labeled plastic bags. The collected dust subsamples were carefully mixed and homogenized into 38 composite samples. The samples were then dried at 50 ◦C for 24 h in an oven followed by sieve analysis using a standard stainless-steel sieve (63 microns).

#### *2.3. Chemical Analyses*

The chemical analyses were performed using the ICP-ES/MS (AQ200) technique in ACME Lab, Vancouver, Canada (ISO 17025 and ISO/IEC 17025). An exact amount of 0.5 g of each household dust sample was leached in modified aqua regia (1: 1: 1 HNO3: HCl: H2O) [49]. Detection limits of Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, V, and Zn were 0.01%, 0.5 ppm, 0.1 ppm, 0.1 ppm, 1 ppm, 0.1 ppm, 0.01%, 0.01 ppm, 1 ppm, 0.1 ppm, 0.1 ppm, 0.1 ppm, 1 ppm, and 1 ppm, respectively.

#### *2.4. Contamination Levels*

#### 2.4.1. Contamination Factor (*C<sup>f</sup>* )

Anthropogenic activities' contribution to PTE contamination has been evaluated using the contamination factor (*C<sup>f</sup>* ). *C<sup>f</sup>* is calculated by the Equation (1) [50].

$$\mathbf{C}\_f^i = \frac{\mathbf{C}\_s^i}{\mathbf{C}\_b^i} \tag{1}$$

where *C i s* is the PTE concentration in analyzed samples, and *C i b* is the background value of the investigated PTE. In this investigation the Upper Continental Crust (UCC) element concentrations [51] were considered as the background values. The *C<sup>f</sup>* values are typically categorized in four distinct classes; class 1 (*C<sup>f</sup>* < 1.0 = low contamination); class 2 (1.0 ≤ *C<sup>f</sup>* < 3.0 = moderate contamination); class 3 (3.0 ≤ *C<sup>f</sup>* ≤ 6.0 = considerable contamination); and class 4 (*C<sup>f</sup>* > 6.0 = very high contamination) [50].

### 2.4.2. Contamination Degree (*Cdeg*)

To detect multielement contamination, *Cdeg* was used. It was calculated for each sampling site using Equation (2) [50].

$$\mathbb{C}\_{\text{deg}} = \sum\_{i=1}^{n} \mathbb{C}\_{f} \tag{2}$$

where *C<sup>f</sup>* is contamination factor, and *n* is the number of the examined PTEs. The *Cdeg* values are typically categorized in four distinct classes; class 1 (*Cdeg* < 6.0 = low contamination); class 2 (6.0 ≤ *Cdeg* < 12.0 = moderate contamination); class 3 (12.0 ≤ *Cdeg* ≤ 24.0 = considerable contamination); and class 4 (*Cdeg* > 24.0 = very high contamination) [50].

#### *2.5. Health Risk Assessment*

PTEs measured in household dust in this investigation are typically known to possess noncarcinogenic effects on human health [52–54]. As, Cd, Cr, Ni, and Pb are believed to possess both noncarcinogenic and carcinogenic effects [52–54]. In the current study, health risks for children and adults in Cairo City were assessed using the noncarcinogenic Hazard Quotient (HQ) of a single element and Hazard Index (HI) of multiple elements via

ingestion, inhalation, and dermal routes of exposure. Furthermore, the Cancer Risk (CR) was calculated using the concentrations of As, Cd, Cr, Ni, and Pb in the collected household dust samples. HQ, HI, and CR were calculated using the calculation model of exposure adopted by USEPA [52–55].

The average daily intakes (ADI) of PTEs in the household dust via nondietary inadvertent ingestion (noncarcinogenic) (*ADIing*), dust inhalation (noncarcinogenic) (*ADIinh*), and dermal contact (noncarcinogenic) (*ADIder*) routes are calculated using Equations (3)–(5) as follows:

$$ADD\_{\rm{ing}} = \frac{\mathbb{C}\_{\rm{s}} \times \text{Ing} \mathbb{R} \times \text{EF} \times \text{ED} \times \text{CF}}{BW \times AT} \tag{3}$$

$$ADI\_{\rm inh} = \frac{\mathcal{C}\_{\rm s} \times Inh \mathcal{R} \times EF \times ED}{\rm PEF \times BW \times AT} \tag{4}$$

$$ADD\_{der} = \frac{\mathbb{C}\_s \times SA \times SL \times ABS \times EF \times ED \times CF}{BW \times AT} \tag{5}$$

The noncarcinogenic risk *HQ* and *HI* of PTEs in the household dust is calculated using Equations (6)–(9) as follows:

$$HQ\_{\rm ing} = \frac{ADI\_{\rm ing}}{RfD\_{\rm ing}}\tag{6}$$

$$HQ\_{\rm inh} = \frac{ADI\_{\rm inh}}{RfD\_{\rm inh}} \tag{7}$$

$$HQ\_{der} = \frac{ADI\_{der}}{RfD\_{der}}\tag{8}$$

$$HI = \sum HQ\_{\text{ing}} + \sum HQ\_{\text{inh}} + \sum HQ\_{\text{der}} \tag{9}$$

The lifetime average daily dose (carcinogenic) (LADD) and the carcinogenic risk (CR) of As, Cd, Cr, Ni, and Pb in household dust is calculated using Equations (10)–(13) as follows:

$$LADD\_{\rm ing} = \left(\frac{\mathbb{C}\_{\rm s} \times EF \times CF}{AT}\right) \times \left(\left(\frac{\text{IngR} \times ED}{BW}\right)\_{Child} + \left(\frac{\text{IngR} \times ED}{BW}\right)\_{Adult}\right) \tag{10}$$

$$LADD\_{\rm inh} = \left(\frac{\mathbb{C}\_{\rm s} \times EF}{AT \times PET}\right) \times \left(\left(\frac{InhR \times ED}{BW}\right)\_{\rm Child} + \left(\frac{InhR \times ED}{BW}\right)\_{\rm Adult}\right) \tag{11}$$

$$\text{LADD}\_{dir} = \left(\frac{\text{C}\_s \times \text{SL} \times \text{ABS} \times \text{EF} \times \text{CF}}{AT}\right) \times \left(\left(\frac{\text{SA} \times \text{ED}}{\text{BW}}\right)\_{\text{Cilid}} + \left(\frac{\text{SA} \times \text{ED}}{\text{BW}}\right)\_{\text{Adult}}\right) \tag{12}$$

$$\mathcal{R} = \left(\sum LADD\_{\text{ing}} \times SLF\_{\text{ing}}\right) + \left(\sum LADD\_{\text{inh}} \times SLF\_{\text{inh}}\right) + \left(\sum LADD\_{\text{der}} \times SLF\_{\text{der}}\right) \tag{13}$$

where all the abbreviations, definitions, and reference values are given and explained in Table 1. If *HI* is less than one, there is no risk of noncarcinogenic effect; if *HI* is greater than one, there is a risk of noncarcinogenic effect. A value of CR less than 1 <sup>×</sup> <sup>10</sup>−<sup>6</sup> is regarded as modest, a value of CR between 1 <sup>×</sup> <sup>10</sup>−<sup>4</sup> and 1 <sup>×</sup> <sup>10</sup>−<sup>6</sup> is regarded within the permissible level, and a value of CR greater than 1 <sup>×</sup> <sup>10</sup>−<sup>4</sup> is likely to be harmful to humans [52–55].


**Table 1.** Definitions and reference values of human health risk model.

#### *2.6. Data Treatment*

Arc GIS (version 10.8.1; 2020) with a raster interpolation technique (Spline-Tension) was used to display the measured PTEs' location and spatial distribution maps in Cairo City. OriginLab (version OriginPro 2021) was used to present descriptive statistics, boxplot figures, and multivariate statistical analyses. Excel (version Microsoft Office 365 16.0.15028.20160) was used to calculate contamination levels and health risk assessment.

#### **3. Results and Discussion**

#### *3.1. PTE Distribution*

This is the first investigation to present a multielement profile of Cairo City household dust. Depending on the study's aims and to guarantee representative sampling, 38 major districts in Cairo City are represented with at least 10 subsamples from each. Table 2 summarizes the descriptive statistical parameters (minimum, maximum, mean, and standard deviation) of the dry weight PTE concentrations in the analyzed indoor household dust samples. Generally, the mean concentrations of these PTEs were ranked in the declining sequence Fe (20,818 ppm) > Al (9092 ppm) > Mn (425 ppm) > Zn (419 ppm) > Cu (116.6 ppm) > Pb (99.3 ppm) > Cr (48.6 ppm) > V (45.7 ppm) > Ni (30.1 ppm) > Co (9.0 ppm) > As (4.0 ppm) > Mo (2.5 ppm) > Cd (1.0 ppm) > Hg (0.30 ppm).

Because there are no PTE guidelines for indoor dusts, our results were compared with the UCC element concentrations [51]. The mean concentrations of As, Cd, Cr, Cu, Hg, Mo, Ni, Pb, and Zn were higher than those of UCC [51], indicating that their sources were affected by anthropogenic activities. CV % indicates the relative variability of element levels

in environmental samples. CV of 20% indicates low variability, CV of 20:50% indicates moderate variability, and CV of 50:100% indicates high variability [61,62]. The CV(%) values of the measured PTEs ranged from 23.9% to 148.1% (Table 2). An interesting point in Table 2 is that Hg exhibited the highest CV value (148.1%), indicating extremely high variability through sampling locations. Cd, Cu, and Pb exhibited relatively higher CV values (51.7, 50.3 and 52.2%, respectively) indicating possible pollution. On the other hand, Al, As, Co, Cr, Fe, Mn, Mo, Ni, V, and Zn showed moderate variability.


**Table 2.** Descriptive statistics of PTEs (ppm) in household dust in Cairo City.

Figure 2 depicts the results of plotting PTE concentrations on spatial distribution maps. Elevated levels (hot spots) of Cd, Cr, Cu, Mo, Ni, Pb, and Zn concentrations were found mostly around eastern, northern, and western regions, which are characterized by higher traffic density, population density, and older buildings. On the other hand, high levels (hot spots) of As, Co, Fe, Mn, and V were mostly concentrated in the southern region, which is characterized by intense industrial activity. A high concentration of Hg was distributed in new Cairo and the northern region.

**Figure 2.** *Cont*.

**Figure 2.** Spatial distribution of PTEs in household dust in Cairo City. **Figure 2.** Spatial distribution of PTEs in household dust in Cairo City.

To put the levels of PTEs in Cairo's indoor dust into perspective, they were compared with the levels of the same elements in indoor dust worldwide (Table 3). Table 3 shows that the mean PTE concentrations in our indoor dust samples were both higher and lower than those worldwide. For instance, Al mean concentration was greater than those reported in Slovenia (Maribor) [63], Greece (Athens) [64], and USA (Texas) [7]. As was higher than those reported in Nigeria (Lagos) [22], Nepal [65], and USA (Texas) [7]. Cd was higher than those reported in Alexandria and Kafr El-Sheikh [45], Saudi Arabia (Riyadh) [1], Qatar (Doha) [66], Nigeria (Lagos) [22], Turkey (Istanbul) [67], Iran (Ahvaz) [60], and Greece (Athens) [64]. Cu was higher than those reported in Kafr El-Sheikh [45], Saudi Arabia (Riyadh) [1], Iraq (Al-Fallujah) [68], Nigeria (Lagos) [22], Iran (Ahvaz) [60], and USA (Texas) [7]. Fe was lower than Qatar (Doha) [66], Nigeria (Lagos) [22], and Canada (Alberta) [69]. Mn was far lower than China (Huize) [12] and Nepal [65]. Ni was higher To put the levels of PTEs in Cairo's indoor dust into perspective, they were compared with the levels of the same elements in indoor dust worldwide (Table 3). Table 3 shows that the mean PTE concentrations in our indoor dust samples were both higher and lower than those worldwide. For instance, Al mean concentration was greater than those reported in Slovenia (Maribor) [63], Greece (Athens) [64], and USA (Texas) [7]. As was higher than those reported in Nigeria (Lagos) [22], Nepal [65], and USA (Texas) [7]. Cd was higher than those reported in Alexandria and Kafr El-Sheikh [45], Saudi Arabia (Riyadh) [1], Qatar (Doha) [66], Nigeria (Lagos) [22], Turkey (Istanbul) [67], Iran (Ahvaz) [60], and Greece (Athens) [64]. Cu was higher than those reported in Kafr El-Sheikh [45], Saudi Arabia (Riyadh) [1], Iraq (Al-Fallujah) [68], Nigeria (Lagos) [22], Iran (Ahvaz) [60], and USA (Texas) [7]. Fe was lower than Qatar (Doha) [66], Nigeria (Lagos) [22], and Canada (Alberta) [69]. Mn was far lower than China (Huize) [12] and Nepal [65]. Ni was higher than those reported in Alexandria

and Kafr El-Sheikh [45], Saudi Arabia (Riyadh) [1], Nigeria (Lagos) [22], Iran (Ahvaz) [60], Greece (Athens) [64], USA (Texas) [7], and Australia (Sydney) [70]. Pb was lower than Egypt (Alexandria) [45], Saudi Arabia (Jeddah) [14], Kuwait [71], Portugal (Estarreja) [25], China (Huize) [12], Nepal [65], Canada (Alberta) [69], and Australia (Sydney) [70]. Zn was higher than those reported in Egypt (Kafr El-Sheikh) [45], Saudi Arabia (Jeddah and Riyadh) [1,14], Iraq (Al-Fallujah) [68], Nigeria (Lagos) [22], Greece (Athens) [64], and USA (Texas) [7].

**Table 3.** Comparison between PTE concentrations in the household dust in Cairo City with those for indoor dust in other cities worldwide.


*n* = Number of Samples; NA = Not Available; \* Median.

#### *3.2. Contamination Levels*

The UCC element concentrations were used as the background values, and the *C<sup>f</sup>* and integrative *Cdeg* indices were applied to objectively analyze the contamination levels in the five administrative regions in Cairo City. The calculated *C<sup>f</sup>* values are presented in Table S2 and Figure 3. Altogether, the five regions were polluted to varying degrees by the measured PTEs. The lowest degrees of pollution were recorded for Al, Co, Fe, Mn, and V, while the highest degrees were recorded for Cd, Cu, Hg, Pb, and Zn, reaching considerably to very high pollution. Hg shows a wide range of *C<sup>f</sup>* values from low to very high pollution.

The calculated *C<sup>f</sup>* -based *Cdeg* values in the investigated five regions (Figure 4) indicate that New Cairo recorded the slightest degree of contamination, ranging from considerably to very high pollution. On the other hand, eastern, northern, western, and southern regions' household dust were very highly polluted.

#### *3.3. Correlations between PTEs*

The multivariate statistical analysis including Pearson's Correlation Coefficient matrix (PCC), Hierarchical Cluster Analysis (HCA) in Q mode, and Principal Component Analysis (PCA) were utilized to reveal and emphasize the correlation intensity and linkage between the analyzed PTEs.

**Figure 3.** (**a**) Boxplots of Cf values: New Cairo; (**b**) eastern region; (**c**) northern region; (**d**) western region; (**e**) southern region; (**f**) all samples. **Figure 3.** (**a**) Boxplots of *C<sup>f</sup>* values: New Cairo; (**b**) eastern region; (**c**) northern region; (**d**) western region; (**e**) southern region; (**f**) all samples.

The calculated Cf-based Cdeg values in the investigated five regions (Figure 4) indicate that New Cairo recorded the slightest degree of contamination, ranging from considerably to very high pollution. On the other hand, eastern, northern, western, and southern re-

gions' household dust were very highly polluted.

**Figure 4.** Boxplots of Cdeg values. **Figure 4.** Boxplots of *Cdeg* values.

*3.3. Correlations Between PTEs*  The multivariate statistical analysis including Pearson's Correlation Coefficient matrix (PCC), Hierarchical Cluster Analysis (HCA) in Q mode, and Principal Component Analysis (PCA) were utilized to reveal and emphasize the correlation intensity and linkage between the analyzed PTEs. Correlations values 0.00–0.19, 0.20–0.39, 0.40–0.59, 0.60–0.79, and 0.80–1.00 can be considered as very weak, weak, moderate, strong, and very strong correlations, respectively [73]. As shown in Table 4, very strong positive correlations were observed between Al–V (Pearson's R = 0.81), As–Co (R = 0.91), As–Fe (R = 0.84), As–Mn (R = 0.86), As–V (R = 0.90), Co–Fe (R = 0.95), Co–Mn (R = 0.97), Co–V (R = 0.87), Cr–Cu (R = 0.88), Cu–Ni (R = 0.81), Fe–Mn (R = 0.97), Fe–V (R = 0.83), Mn–V (R = 0.81), and Ni–Zn (R = 0.87). Strong positive correlations were observed between Al–As (R = 0.78), Al–Co (R = 0.67), Al–Zn (R = 0.63), Cd–Cu (R = 0.69), Cd–Ni (R = 0.62), Cd–Pb (R = 0.65), Cd–Zn (R = 0.61), Cr–Mo (R = 0.79), Cr–Ni (R = 0.67), Cr–Pb (R = 0.64), Cu–Mo (R = 0.66), Cu–Pb (R = 0.79), Cu–Zn (R = 0.68), Mo–Ni (R = 0.67), Ni–Pb (R = 0.79), and Pb–Zn (R = 0.67). The most significant finding Correlations values 0.00–0.19, 0.20–0.39, 0.40–0.59, 0.60–0.79, and 0.80–1.00 can be considered as very weak, weak, moderate, strong, and very strong correlations, respectively [73]. As shown in Table 4, very strong positive correlations were observed between Al–V (Pearson's R = 0.81), As–Co (R = 0.91), As–Fe (R = 0.84), As–Mn (R = 0.86), As–V (R = 0.90), Co–Fe (R = 0.95), Co–Mn (R = 0.97), Co–V (R = 0.87), Cr–Cu (R = 0.88), Cu–Ni (R = 0.81), Fe–Mn (R = 0.97), Fe–V (R = 0.83), Mn–V (R = 0.81), and Ni–Zn (R = 0.87). Strong positive correlations were observed between Al–As (R = 0.78), Al–Co (R = 0.67), Al–Zn (R = 0.63), Cd–Cu (R = 0.69), Cd–Ni (R = 0.62), Cd–Pb (R = 0.65), Cd–Zn (R = 0.61), Cr–Mo (R = 0.79), Cr–Ni (R = 0.67), Cr–Pb (R = 0.64), Cu–Mo (R = 0.66), Cu–Pb (R = 0.79), Cu–Zn (R = 0.68), Mo–Ni (R = 0.67), Ni–Pb (R = 0.79), and Pb–Zn (R = 0.67). The most significant finding that can be deduced from these positive linear relations is the role played by Al, Fe, and Mn as scavenging elements in the distribution of PTEs, especially As, Co, V, and Zn [48,74]. The strong to very strong positive correlation between the measured PTEs indicates their close distribution and association and may suggest a shared source. It appears to imply that household dust with more elevated levels of one toxic element additionally contain higher levels of other PTEs.

that can be deduced from these positive linear relations is the role played by Al, Fe, and Mn as scavenging elements in the distribution of PTEs, especially As, Co, V, and Zn [48,74]. The strong to very strong positive correlation between the measured PTEs indicates their close distribution and association and may suggest a shared source. It appears to imply that household dust with more elevated levels of one toxic element additionally contain higher levels of other PTEs. HCA (Figure 5) reduced data into two main clusters. Cluster (1) includes: (a) Al, As, and V and (b) Co, Mn, and Fe. Cluster (2) was subdivided into (c) Cd, Ni, Zn, and Pb; (d) Cr, Cu, and Mo; and (E) Hg. Figure 6 presents the PCA component. Three components, PC1 (49.60%; eigenvalue 6.44), PC2 (24.87%; eigenvalue 3.48), and PC3 (410.40%; eigenvalue 1.46), were extracted from PCA. The 3D plotting of the extracted three components positively confirms the association between Al, As, Co, Fe, Mn, and V (Figure 6a). The 2D plotting of PC1 and PC2 combined with sampling sites (Figure 6b) indicates that Al, As, Co, Fe, Mn, and V are more associated together in the southern region samples. It can be concluded that these elements originated from natural sources; this is in agreement with [22,75]. As enriched from intensive industrial activity in the southern region and adsorbed on Fe–Mn oxides surface [76].

**Table 4.** PCC matrix for PTEs in the investigated household dust (*n* = 38). Mo 1.00 0.67 0.56 0.32 0.30 Ni 1.00 0.79 0.55 0.87

Mn 1.00 0.42 0.51 0.12 0.81 0.35

*Toxics* **2022**, *10*, x FOR PEER REVIEW 13 of 23

 **Al As Cd Co Cr Cu Fe Hg Mn Mo Ni Pb V Zn**  Al 1.00 0.78 0.26 0.67 −0.03 0.10 0.56 0.06 0.57 0.03 0.51 0.27 0.81 0.63 As 1.00 0.28 0.91 −0.01 0.10 0.84 −0.09 0.86 0.22 0.50 0.11 0.90 0.49 Cd 1.00 0.24 0.59 0.69 0.27 0.30 0.22 0.42 0.62 0.65 0.35 0.61 Co 1.00 0.09 0.11 0.95 −0.13 0.97 0.33 0.49 0.09 0.87 0.40 Cr 1.00 0.88 0.27 0.07 0.14 0.79 0.67 0.64 0.11 0.39 Cu 1.00 0.25 0.13 0.14 0.66 0.81 0.79 0.16 0.68 Fe 1.00 −0.16 0.97 0.54 0.58 0.21 0.83 0.35

**Table 4.** PCC matrix for PTEs in the investigated household dust (*n* = 38).

**Figure 5.** HCA dendrogram. **Figure 5.** HCA dendrogram.

**Figure 6.** (**a**) PCA variable loading: 3D loading between the extracted 3 components; (**b**) 2D loading between PC1 and PC2 combined with sampling sites. **Figure 6.** (**a**) PCA variable loading: 3D loading between the extracted 3 components; (**b**) 2D loading between PC1 and PC2 combined with sampling sites.

PTEs in household dust can be attributed to indoor activities such as cooking, smoking, carpet, paper, clothing, cosmetic and personal care products, electric instruments, and cleaning products [65,71,77,78]. A substantial portion of the PTEs emitted by various outdoor activities can travel considerable distances via atmospheric particulate matter and enter the indoor environment in a variety of ways [71]. Al is geochemically stable, while Fe and Mn are geochemically related elements that are abundant in the earth's crust and considered as major elements in soil minerals. The weathering of pre-existing rocks, sediments, and soils primarily releases these major elements [22,71,79] because the levels of PTEs in household dust can be attributed to indoor activities such as cooking, smoking, carpet, paper, clothing, cosmetic and personal care products, electric instruments, and cleaning products [65,71,77,78]. A substantial portion of the PTEs emitted by various outdoor activities can travel considerable distances via atmospheric particulate matter and enter the indoor environment in a variety of ways [71]. Al is geochemically stable, while Fe and Mn are geochemically related elements that are abundant in the earth's crust and considered as major elements in soil minerals. The weathering of pre-existing rocks, sediments, and soils primarily releases these major elements [22,71,79] because the levels of Al, Fe, and Mn in the investigated household dust samples are not polluted and relatively

Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribu-

8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

(5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively.

(5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively.

Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribu-

8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

(5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively.

(5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively.

Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribu-

8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

(5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively.

(5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively.

deficient. These elements are probably of predominantly geogenic origin and were not enriched in the dust samples by anthropogenic activities. Some exceptions for Mn were recognized in some sites moderately polluted with Mn. Mn can be enriched by many anthropogenic sources such as Mn fungicides [80], Mn–Ni batteries [81], and pigment and paints [82]. Similarly, Co and V concentrations in the majority of the studied samples are below background levels and show a low degree of pollution, indicating that they originated from natural sources before being transported and settling in household dust. *Toxics* **2022**, *10*, x FOR PEER REVIEW 16 of 23 *Toxics* **2022**, *10*, x FOR PEER REVIEW 16 of 23 *Toxics* **2022**, *10*, x FOR PEER REVIEW 16 of 23

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Anthropogenic sources of As, Cd, Cr, Cu, Ni, Pb, and Zn include traffic emissions, braking engine wear, corrosion of vehicle parts, lubricating oils, coal, and fossil fuel combustion, building and construction materials, rubbers, pesticides, and industrial emissions [19,22,63,71,75,77,81,83]. Cr and Zn can be sourced from wood preservative furniture [12,65]. Chemical and pharmaceutical industries, coal combustion, municipal solid waste incineration, and cement manufacture are all anthropogenic sources of Hg. Building materials (interior decorations, paints, and fluorescent lamps), household appliances and electronic devices, LCD displays, monitors, batteries, clothes dryers, irons, washing machines, fluorescent bulbs, neon lights, and thermometers are other potential indoor sources [84].

#### *3.4. Health Risk Assessment*

Results of human health risk assessment show that the calculated *HQing*, *HQder*, and *HQinh* values for individual element (Table S3) and combined PTEs (Table 5; Figure 7a,b) in the household dust were less than one for children and adults. In addition, HI values for adults of the combined PTEs in the household dust were less than one, suggesting no potential noncancer risks (Table 5; Figure 7b). On the other hand, HI values for children were greater than those for adults; one site (site 16; Eastern region) recorded HI values higher than one, suggesting potential noncancer risks for children (Figure 7a). **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10– 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 × 10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribution (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd (5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively. *HQing* was most likely to pose a noncancer risk of more than **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10– 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 × 10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribution (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd (5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively. *HQinh* and **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10– 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 × 10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribution (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd (5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively. *HQder*; this is consistent with several research findings [1,4,12,59,64,85]. The calculated individual element contribution (%) for children and adults noncarcinogenic risk revealed no differences in their contributions in the two age groups. As a result, we discuss them all together. Individual element contribution (%) for noncarcinogenic risk **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10– 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 × 10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribu-*HQing*, **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10– 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 × 10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribu-*HQder*, and **Figure 7.** (**a**) Boxplots of noncancer risk for children; **b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10– 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 × 10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribu-*HQinh* is presented in Figure 7c.In's ingestion route elements' contribution is as follows: Pb (30.53%) > Cr (17.41%) > As (14.38%) > Mn (11.44%) > Al (9.78%) > V (7.03%) > Cu (3.14%) > Ni (1.61%) > Zn (1.50%) > Cd (1.07%) > Hg (1.07%) > Mo (0.54%) > Co (0.48) (Figure 8). For dermal contact route, elements' contribution is as follows: As (31.66%) > Cr (26.19%) > V (21.15%) > Mn (7.48%) > Pb (7.12%) > Cd (3.22%) > Al (2.94%) > Hg (0.46%) > Cu (0.31%) > Zn (0.26%) > Ni (0.18%) > Mo (0.04%) > Co (0.02). For respiratory inhalation route, the contribution of Mn in **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability *HQinh* values was the largest, reaching 75.43%, followed by Al (16.12%), Cr (4.30%), and Co (3.99%).

tion (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure

tion (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure

Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

(5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively.

Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10–

8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) Pb (1.02%) > 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; **Table 5.** Integrated noncancer and cancer risks values. **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual


tion (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure

Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

(5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively.

(5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively.

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**Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk.

**Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual

Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 × 10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants

were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10–

tion (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribution (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

(5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively.

In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10– 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 × 10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribution (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd (5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively. In terms of carcinogenic risk, *LADDing*, *LADDder*, and *LADDinh* values for individual elements were in the safe limit (Table S4). In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). <sup>⅀</sup>LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10– 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 × 10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribution (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd (5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively. *LADDing* values for As, Cd, Cr, Ni, and Pd were higher than 1 <sup>×</sup> <sup>10</sup>−<sup>4</sup> in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10– 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 × 10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribution (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > *LADDder* values for As and Cr were higher than <sup>1</sup> <sup>×</sup> <sup>10</sup>−6, and **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10– 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 × 10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribution (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure *LADDinh* values for As, Cd, Cr, Ni, and Pd were lower than 1 <sup>×</sup> <sup>10</sup>−<sup>6</sup> (Figure 8a; Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 <sup>×</sup> <sup>10</sup>−<sup>4</sup> in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-to-mouth ingestion > dermal contact > respiratory inhalation. Individual element contribution (%) for carcinogenic risk **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10– 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; *LADDing*, **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10– 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; *LADDder*, and **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10– 6, and ⅀LADDinh values for As, Cd, Cr, Ni, and Pd were lower than 1 × 10–6 (Figure 8a; *LADDinh* is presentedin Figure 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd (5.40%) > Pb (3.59%) in **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd (5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively. *LADDing*, **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd (5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively. *LADDder*, and **Figure 7.** (**a**) Boxplots of noncancer risk for children; (**b**) for adults; (**c**) pie chart showing individual element contribution (%) for noncarcinogenic risk. In terms of carcinogenic risk, LADDing, LADDder, and LADDinh values for individual elements were in the safe limit (Table S4). ⅀LADDing values for As, Cd, Cr, Ni, and Pd (5.40%) > Pb (3.59%) in ⅀LADDing, LADDder, and ⅀LADDinh, respectively. *LADDinh*, respectively.

Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 × 10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants

were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10–

Table 5). Alarmingly, CR values through the three routs of exposure were higher than 1 × 10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants

were higher than 1 × 10–4 in the majority of the investigated sites, indicating a probability of cancer risk. On the other hand, ⅀LADDder values for As and Cr were higher than 1 × 10–

tion (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribution (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

(5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively.

tion (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

10–4 in the majority of the investigated sites, indicating a possible cancer risk to inhabitants in Cairo City. The CR risks via various exposure pathways were as follows: hand-tomouth ingestion > dermal contact > respiratory inhalation. Individual element contribution (%) for carcinogenic risk ⅀LADDing, ⅀LADDder, and ⅀LADDinh is presented in Figure 8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

8b. The elements' contributions are Ni (61.84%) > Cr (29.39%) > As (7.28%) > Pb (1.02%) > Cd (0.46%), As (81.93%) > Cr (18.07%), and As (52.14%) > Ni (21.73%) > Cr (17.14%) > Cd

(5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively.

(5.40%) > Pb (3.59%) in ⅀LADDing, ⅀LADDder, and ⅀LADDinh, respectively.

**Figure 8.** (**a**) Boxplots of cancer risk; (**b**) pie chart showing individual element contribution (%) for cancer risk. **Figure 8.** (**a**) Boxplots of cancer risk; (**b**) pie chart showing individual element contribution (%) for cancer risk.

The spatial distribution maps of the calculated HI (children), HI (adults), and CR risks are presented (Figure 9) to inform decision makers about the riskiest districts so that mitigation measures could be implemented. The presented maps show the same distribution for noncancer and cancer risk, with hot spots concentrated in the eastern, northern, and western regions due to condensed road networks in these regions with permanent traffic congestion (Figure 1). In addition, the southern region showed considerable risk distribution due to the intensive industrial activity in this region. One of the most significant limitations of this investigation is the analysis of few composed samples and the undetermined indoor microenvironments. Additional investigation in highly polluted regions should include specific indoor microenvironments such as entrances, kitchens, living rooms, children's rooms, and bedrooms to provide a more comprehensive analysis of household dust geochemistry in various microenvironments and to differentiate between PTE outdoor and indoor sources. The spatial distribution maps of the calculated HI (children), HI (adults), and CR risks are presented (Figure 9) to inform decision makers about the riskiest districts so that mitigation measures could be implemented. The presented maps show the same distribution for noncancer and cancer risk, with hot spots concentrated in the eastern, northern, and western regions due to condensed road networks in these regions with permanent traffic congestion (Figure 1). In addition, the southern region showed considerable risk distribution due to the intensive industrial activity in this region. One of the most significant limitations of this investigation is the analysis of few composed samples and the undetermined indoor microenvironments. Additional investigation in highly polluted regions should include specific indoor microenvironments such as entrances, kitchens, living rooms, children's rooms, and bedrooms to provide a more comprehensive analysis of household dust geochemistry in various microenvironments and to differentiate between PTE outdoor and indoor sources.

**Figure 9.** Spatial distribution of HI for children and adults and CR risks for the household dust exposure in Cairo City. **Figure 9.** Spatial distribution of HI for children and adults and CR risks for the household dust exposure in Cairo City.

#### **4. Conclusions 4. Conclusions**

This study is the first one to comprehensively measure the chemical composition of household dust in Cairo City, Egypt. In general, the following important conclusions can be gained: This study is the first one to comprehensively measure the chemical composition of household dust in Cairo City, Egypt. In general, the following important conclusions can be gained:


**Supplementary Materials:** The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/toxics10080466/s1, Table S1: Samples distribution in administrative regions and districts in Cairo City.; Table S2: Calculated *C<sup>f</sup>* and *Cdeg* values; Table S3: Calculated noncancer *HQing*, *HQder*, and *HQinh* values. Table S4: Calculated cancer *LADDing*, *LADDder*, and *LADDinh* values.

**Author Contributions:** Conceptualization, A.G., H.I.F. and S.M.A.E.B.; methodology, A.G., A.S., H.I.F. and S.M.A.E.B.; software, A.G., H.I.F. and S.M.A.E.B.; validation, A.G., H.I.F. and S.M.A.E.B.; formal analysis, A.G. and A.S.; investigation, A.G., H.I.F. and S.M.A.E.B.; resources, A.G. and A.S.; data curation, A.G., H.I.F. and S.M.A.E.B.; writing—original draft preparation, A.G., H.I.F. and S.M.A.E.B.; writing—review and editing, A.G., A.S. and Y.H.D.; supervision, A.G., A.S. and Y.H.D.; project administration, A.S.; funding acquisition, A.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This paper is passed upon work supported by the Science, Technology & Innovation Funding Authority (STDF), Egypt, Under Grant Number: 41628.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** This paper is passed upon work supported by Science, Technology & Innovation Funding Authority (STDF), Egypt, under Grant Number: 41628. Therefore, the authors gratefully acknowledge technical and financial support from the Science, Technology & Innovation Funding Authority (STDF), Egypt. Thanks also to A R Abu Zeid (Assiut University, New Valley Branch) for providing Landsat data and helping in the application of the GIS technique.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

#### **References**

